Hydraulic pumps are used in many applications. In the oil and gas industry, one application is use of a hydraulic pump to power a hydraulic motor to turn a drill pipe. A specific example of this application is a power swivel, which is used to turn the drill pipe while suspended in the drilling.
In power swivel applications, the pump is typically powered by a diesel engine or electric motor. The pumps in commercial use are usually infinitely variable displacement models which provide infinitely variable speed for the power swivel. However, these pumps are not particularly robust and are subject to failure, often by fluid contamination, if not adequately maintained by changing out the filters.
Gear pumps provide a much more robust and contamination friendly design, but their use has not been favored because of difficulties in controlling their output. A control system which permits good control would enable gear pumps to be used for power swivel applications. It is an object of this invention to provide such a control system.